Methods and system for wavelength tunable optical components and sub-systems

ABSTRACT

Wavelength division multiplexing (WDM) has enabled telecommunication service providers to provide multiple independent multi-gigabit channels on one optical fiber. To Microoptoelectromechanical systems (MOEMS) integrating optical waveguides upon a MEMS can provide further integration opportunities and functionality options. Improvements to the design and implementation of MOEMS devices are presented where monolithically integrated optical waveguides are directly supported, moved and/or deformed upon a beam coupled to and manipulated by a MEMS. Accordingly, such MOEMS can provide programmable functionality by enabling alignment of the optical waveguide upon the MEMS to one of multiple optical waveguides disposed relative to the moving facet of the rotating optical waveguide.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority as a divisional patent application ofU.S. patent application Ser. No. 15/124,198 filed Sep. 7, 2016 entitled“Methods and System for Wavelength Tunable Optical Components andSub-Systems”, which itself claims the benefit of priority as a 371National Phase application of PCT/CA2015/000,135 filed Mar. 9, 2015entitled “Methods and System for Wavelength Tunable Optical Componentsand Sub-Systems”, which itself claims priority from U.S. ProvisionalPatent Application US 62/037,655 filed Aug. 15, 2014 entitled “Methodsand Systems for Microelectromechanical Packaging”, U.S. ProvisionalPatent Application 61/950,238 filed Mar. 10, 2014 entitled “Methods andSystems Relating to Optical Networks”, and U.S. Provisional PatentApplication 61/949,484 filed Mar. 7, 2014 entitled “Methods and Systemfor Wavelength Tunable Optical Components and Sub-Systems”, the entirecontents of which are incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to microoptoelectromechanical systems (MOEMS) andmore particular to designs and enhancements for opticalmicroelectromechanical systems (MEMS) waveguides and mirrors as well asoptical components exploiting such optical MEMS elements.

BACKGROUND OF THE INVENTION

Wavelength division multiplexing (WDM) has enabled telecommunicationservice providers to fully exploit the transmission capacity of opticalfibers in their core network. State of the art systems in long-haulnetworks now have aggregated capacities of terabits per second.Moreover, by providing multiple independent multi-gigabit channels, WDMtechnologies offer service providers with a straight forward way tobuild networks and expand networks to support multiple clients withdifferent requirements. At the same time these technologies have evolvedfrom long haul networks down to the access networks as well as into datacenters, to support the continuing inexorable demand for data. In orderto reduce costs, enhance network flexibility, reduce spares, and providereconfigurability many service providers have migrated away from fixedwavelength transmitters, receivers, and transceivers, to wavelengthtunable transmitters, receivers, and transceivers as well as wavelengthdependent add-drop multiplexers, space switches etc. However, to meetthe competing demands for improved performance, increased integration,reduced footprint, reduced power consumption, increased flexibility,reconfigurability, and lower cost the prior art solutions using discretecomponents must be superseded. Accordingly, within the technologies toexploit/adopt are monolithic optical circuit technologies, hybridoptoelectronic integration, microelectromechanical systems (MEMS), andmicrooptoelectromechanical systems (MOEMS).

An essential MOEMS element in a WDM system is a MOEMS mirror orwaveguide capable of deflection under electronic control. However,unlike most MEMS device configurations where the MEMS is simply used toswitch between positions, when the MEMS includes an optical waveguide,the state of MOEMS becomes important in all transition positions. Thecharacteristics of the MEMS determines the characteristics of the WDMsystem in that it affects the number of wavelength channels and thedynamic wavelength switching capabilities of the system. The role of theMEMS becomes essential in an integrated photonic device such as it isresponsible not only for altering the paths of light but directing lightthrough a plurality of wavelength filters which allows the reflection ortransmission of a dedicated, mono-chromatic light.

Accordingly, it would be beneficial to improve the performance of suchMEMS and thereby the performance of the optical components and opticalsystems they form part of. Beneficially, the inventors have establisheda range of improvements to the design and implementation of such MOEMSmirrors and MOEMS waveguides as well as optical waveguide technologiessupporting the extension of these device concepts in datacom, telecom,sensors, optical delay lines, and mid-infrared optical spectroscopy forexample.

Other aspects and features of the present invention will become apparentto those ordinarily skilled in the art upon review of the followingdescription of specific embodiments of the invention in conjunction withthe accompanying figures.

SUMMARY OF THE INVENTION

It is an object of the present invention to mitigate limitations in theprior art relating to microoptoelectromechanical systems (MOEMS) andmore particular to designs and enhancements for opticalmicroelectromechanical systems (MEMS) waveguides and mirrors as well asoptical components exploiting such optical MEMS elements.

In accordance with an embodiment of the invention there is provided adevice comprising:

-   -   an optical waveguide structure comprising a first predetermined        portion formed from a plurality of three-dimensional (3D)        optical waveguides for routing an optical signal upon a        substrate and a second predetermined portion comprising a        two-dimensional (2D) optical waveguide for routing the optical        signals from a first subset of the plurality of 3D optical        waveguides to a second subset of the plurality of 3D optical        waveguides; and    -   a rotational microoptoelectromechanical (MOEMS) element        comprising a pivot, an actuator, and the 2D optical waveguide;        wherein    -   a predetermined rotation of the MOEMS element under the motion        of the actuator results in the coupling configuration between an        optical waveguide of the first subset of the plurality of 3D        optical waveguides being coupled to a predetermined optical        waveguide within the second subset of the plurality of 3D        optical waveguides.

In accordance with an embodiment of the invention there is provided adevice comprising:

-   -   a rotatable MEMS element forming a predetermined portion of a        wavelength tunable reflector having an optical waveguide for        coupling optical signals to and from the wavelength tunable        reflector;    -   a reflective optical gain block coupled to the optical        waveguide; wherein    -   the rotatable MEMS element sets the wavelength tunable reflector        in dependence upon selection of a wavelength reflective filter        from a plurality of wavelength reflective filters by rotation of        the rotatable MEMS element wherein the optical signals propagate        within a planar waveguide forming a first predetermined portion        of the MEMS element and are reflected by a mirror forming a        second predetermined portion of the MEMS element.

In accordance with an embodiment of the invention there is provided arotatable MEMS element which is coupled to a rotational actuator forcontrolling the rotation of the rotatable MEMS element and a linearactuator for translating the rotatable MEMS element away from a facet ofthe optical waveguide thereby allowing rotational position setting ofthe rotatable MEMS actuator prior to re-engaging the rotatable MEMSelement against the facet of the optical waveguide.

In accordance with an embodiment of the invention there is provided arotatable MEMS element comprising at least one first feature upon asurface of the rotatable MEMS element comprising a planar waveguide anda plurality of second features mating to the first feature disposed upona facet of a device such that the at least one first feature can bemated to a predetermined second feature of the plurality of secondfeatures once the rotating MEMS element has been rotated to apredetermined position.

In accordance with an embodiment of the invention there is provided adevice comprising:

-   -   an optical waveguide coupled to an optical network for receiving        optical signals; and    -   an optical detector coupled to the optical network; wherein    -   the optical signals coupled to the optical detector are        wavelength filtered in dependence upon selection of a wavelength        reflective filter from a plurality of wavelength reflective        filters by rotation of the rotatable MEMS element wherein the        optical signals propagate within a planar waveguide forming a        first predetermined portion of the MEMS element and are        reflected by a mirror forming a second predetermined portion of        the MEMS element.

In accordance with an embodiment of the invention there is provided adevice comprising:

-   -   a rotatable MEMS element forming a predetermined portion of a        wavelength tunable reflector having an optical waveguide for        coupling optical signals to and from the wavelength tunable        reflector;    -   an optical coupler coupled to the optical waveguide and having a        first port coupled to an optical network for receiving optical        signals and coupling them to the optical waveguide and a second        port for coupling optical signals from the optical waveguide;        and    -   an optical detector coupled to the second port; wherein    -   the optical signals coupled to the optical detector are        wavelength filtered in dependence upon selection of a wavelength        reflective filter from a plurality of wavelength reflective        filters by rotation of the rotatable MEMS element wherein the        optical signals propagate within a planar waveguide forming a        first predetermined portion of the MEMS element and are        reflected by a mirror forming a second predetermined portion of        the MEMS element.

In accordance with an embodiment of the invention there is provided adevice comprising:

-   -   a rotatable MEMS element forming a predetermined portion of a        wavelength filter having an optical waveguide for coupling        optical signals to and from the wavelength tunable filter;    -   an optical coupler coupled to the optical waveguide for        receiving optical signals and coupling them to the optical        waveguide;    -   an optical detector coupled to the output of the wavelength        filter; wherein    -   the optical signals coupled to the optical detector are        wavelength filtered in dependence upon selection of a wavelength        filter from a plurality of wavelength filters by rotation of the        rotatable MEMS element wherein the optical signals propagate        within a planar waveguide forming a first predetermined portion        of the MEMS element and are reflected by a mirror forming a        second predetermined portion of the MEMS element.

In accordance with an embodiment of the invention there is provided adevice comprising:

-   -   an optical waveguide structure comprising a first predetermined        portion formed from a plurality of three-dimensional (3D)        optical waveguides for routing an optical signal upon a        substrate and a second predetermined portion comprising an input        3D optical waveguide for routing the optical signals from a        first subset of the plurality of 3D optical waveguides to a        second subset of the plurality of 3D optical waveguides; and    -   a rotational microoptoelectromechanical (MOEMS) element        comprising a pivot, an actuator, and the input 3D optical        waveguide; wherein    -   a predetermined rotation of the MEMS element under the motion of        the actuator results in the alignment of the input 3D optical        waveguide with a predetermined 3D optical waveguide of the first        subset of the plurality of 3D optical waveguides.

In accordance with an embodiment of the invention there is provided adevice comprising:

-   -   an optical waveguide structure comprising at least first and        second three-dimensional (3D) optical waveguides for routing an        optical signal upon a substrate and a second predetermined        portion comprising a two-dimensional (2D) optical waveguide for        routing optical signals with respect to the first and second 3D        optical waveguides; and    -   a rotational microoptoelectromechanical (MOEMS) element        comprising a pivot, an actuator, the 2D optical waveguide, and        an optical grating; wherein    -   a predetermined rotation of the MEMS element under the motion of        the actuator results in optical signals within a predetermined        wavelength range coupled from the first 3D optical waveguide to        the second 3D optical waveguide via the 2D optical waveguide and        optical grating.

Other aspects and features of the present invention will become apparentto those ordinarily skilled in the art upon review of the followingdescription of specific embodiments of the invention in conjunction withthe accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way ofexample only, with reference to the attached Figures, wherein:

FIG. 1A depicts examples of prior art fixed wavelength and wavelengthtunable sources;

FIG. 1B depicts an example of a wavelength tunable source according toan embodiment of the invention;

FIG. 2 depicts a wavelength tunable source according to an embodiment ofthe invention;

FIG. 3 depicts cross-sections of the MEMS mirror and optical waveguideinterface according to embodiments of the invention exploiting siliconnitride and silicon-on-insulator waveguide technologies;

FIG. 4 depicts exemplary designs and channel counts for MEMS mirroractuated waveguide interrogators exploiting silicon nitride waveguidesaccording to embodiments of the invention;

FIG. 5 depicts exemplary designs and channel counts for MEMS mirroractuated waveguide interrogators exploiting silicon-on-insulatorwaveguides according to embodiments of the invention;

FIGS. 6 through 9 depict an exemplary process flow for the manufactureof a MEMS mirror actuated Bragg waveguide interrogator exploitingsilicon nitride waveguides according to an embodiment of the invention;

FIGS. 10A and 10B depict exemplary fabricated MEMS mirrors with theirelectrostatic comb actuators according to an embodiment of theinvention;

FIG. 11A depicts an exemplary wavelength selective MOems-TUunableSilicon (MOTUS) optical engine according to an embodiment of theinvention;

FIG. 11B depicts an exemplary wavelength selective MOTUS optical engineaccording to an embodiment of the invention;

FIG. 12A depicts an exemplary wavelength selective MOTUS optical engineaccording to an embodiment of the invention;

FIG. 12B depicts an exemplary wavelength selective MOTUS optical engineaccording to an embodiment of the invention;

FIG. 13 depicts a Reconfigurable Optical Add-Drop Module (ROADM)exploiting MOTUS optical engines to select a wavelength or a group ofwavelengths according to an embodiment of the invention;

FIG. 14 depicts cross-sections through wavelength selective MOTUSoptical engines according to an embodiment of the invention with hybridflip-chip assembly of a semiconductor optical gain block with siliconnitride core waveguides;

FIG. 15A depicts cross-sections through wavelength selective MOTUSoptical engines according to an embodiment of the invention with hybridflip-chip assembly of a semiconductor optical gain block with siliconcore waveguides;

FIG. 15B depicts cross-sections through wavelength selective MOTUSoptical engines according to an embodiment of the invention with hybridbutt coupling assembly of a semiconductor optical gain block with MOTUSwhere anti-reflectivity is improved by way of the combination of anangle in the waveguide in the gain block and anti-reflectivity coatingson the gain block, MOTUS or both;

FIG. 16 depicts a wavelength selective MOTUS optical engine according toan embodiment of the invention with hybrid integration of discretesemiconductor optical gain block and external Mach-Zehnder modulator;

FIG. 17 depicts maximum modulation speed versus cavity length for anexternal cavity laser comprising a semiconductor optical gain block witha wavelength selective MOTUS optical engine for wavelength setting forboth silicon nitride and silicon waveguide cores;

FIG. 18 depicts a wavelength selective MOTUS optical engine according toan embodiment of the invention with hybrid integration of amonolithically integrated semiconductor optical gain block and externalMach-Zehnder modulator die;

FIG. 19 depicts a wavelength selective MOTUS optical engine according toan embodiment of the invention with post-wavelength filter detectors;

FIG. 20 depicts a wavelength selective MOTUS optical engine according toan embodiment of the invention acting a wavelength selective receiver;

FIG. 21 depicts a wavelength selective receiver according to anembodiment of the invention exploiting a wavelength selective MOTUSoptical engine with Bragg grating based transmissive Fabry-Perot filtersand coupler combiners;

FIG. 22 depicts a wavelength selective receiver according to anembodiment of the invention exploiting a wavelength selective MOTUSoptical engine with Bragg grating based transmissive Fabry-Perot filtersand coupler combiners; and

FIG. 23 depicts cross-sections through a wavelength selective opticaltransmitter according to an embodiment of the invention incorporatingintegrated semiconductor die with semiconductor optical gain blocks,high reflectivity mirror, and external Mach-Zehnder filter;

FIGS. 24A to 24C depict cross-sections of alternate structures for aMOEMS according to embodiments of the invention;

FIG. 25 depicts a lateral waveguide micro-positioner design according toan embodiment of the invention for the alignment/misalignment of anoptical waveguide with another optical waveguide or optical component;

FIG. 26 depicts a waveguide micro-positioner design according to anembodiment of the invention for the alignment/misalignment of an opticalwaveguide with another optical waveguide or optical component asemployed in the manipulation of a silicon nitride-on-silicon waveguidewithin a MOEMS exploiting MEMS micro-positioners;

FIGS. 27A and 27B depict wavelength tunable dual-band transceivers fornext generation networks exploiting wavelength selective MOTUS opticalengines with Bragg grating based transmissive and reflective filters inconjunction with InP optical amplifiers, APDs, and Mach-Zehndermodulator;

FIG. 28A depicts a wavelength tunable dual-band transceivers for nextgeneration networks employing optical coherent receiver for thedownstream link;

FIG. 28B depicts a wavelength tunable dual-band QPSK transceivers fornext generation networks exploiting wavelength selective MOTUS opticalengines with Bragg grating based transmissive and reflective filters inconjunction with InP optical amplifiers, APDs, and Mach-Zehndermodulators;

FIGS. 29A and 29B depict an alternate waveguide to wavelength selectivefilter coupling mechanism according to embodiments of the inventionexploiting direct waveguide coupling from the tilted beam of a MEMSactuator;

FIG. 30 depicts an alternate exemplary wavelength selective MOTUSoptical engine according to an embodiment of the invention.

DETAILED DESCRIPTION

The present invention is directed to microoptoelectromechanical systems(MOEMS) and more particular to designs and enhancements for opticalmicroelectromechanical systems (MEMS) waveguides and mirrors as well asoptical components exploiting such optical MEMS elements.

The ensuing description provides exemplary embodiment(s) only, and isnot intended to limit the scope, applicability or configuration of thedisclosure. Rather, the ensuing description of the exemplaryembodiment(s) will provide those skilled in the art with an enablingdescription for implementing an exemplary embodiment. It beingunderstood that various changes may be made in the function andarrangement of elements without departing from the spirit and scope asset forth in the appended claims.

Within this specification the inventors refer to optical waveguideswhich are planar, confined vertically, but not confined laterally astwo-dimensional (2D) optical waveguides (2D) and those opticalwaveguides which are further confined laterally and vertically asthree-dimensional (3D) optical waveguides.

Wavelength Tunable Optical Source

As noted supra wavelength tunable optical sources and/or receivers havesignificant benefit in the provisioning of transmitters, receivers, andtransceivers within todays optical communication networks and evolvingrequirements for optical networks with dynamic wavelength allocation,reduced installation complexity, single line card designs, andreconfigurability. Within the prior art several approaches have beenemployed to date and whilst these have demonstrated high performancetransmitters, they suffer limitations such as assembly complexity,achievable performance, and high cost. Two such prior art approaches aredepicted in second and third images 100B and 100C respectively incomparison to a standard fixed wavelength laser source in first image100A in FIG. 1A.

In first image 100A a fixed wavelength laser source is depicted in adual-in line (DIL) package configuration and comprises monitorphotodiode (not identified for clarity) and laser diode die 111 mountedupon a chip carrier 112 which comprises a thermistor (not identified forclarity) for monitoring the temperature as the laser diode die 111 has afast wavelength versus temperature profile. The output of the laserdiode die 111 is coupled via an optical lens—optical isolator assembly113 such that is focused at a location 113 wherein the optical fiberwithin a ferrule assembly 114, for example, is positioned and assembledto couple the optical signal to the network via optical fiber pigtail115. The laser diode die 111 may, for example, be a distributed feedback(DFB) laser, a distributed Bragg reflector (DBR) laser or a monolithicexternally modulated DFB laser.

Accordingly, in second image 100B a wavelength settable transmitterassembly prior to optical fiber pigtailing and sealing is depicted. Asshown the assembly comprises a laser array 121, MEMS switch array 122,monitor photodiode 123 and wavelength locker 124. The wavelength locker124 provides a means of locking the laser array 121 to a predeterminedgrid, such as 100 GHz C-band grid of long-haul telecommunications around1550 nm. Accordingly, the laser array 121 comprises an array of opticalsources monolithically integrated into the same semiconductor die, e.g.40 DFB lasers. The provisioning of the selected wavelength for thetransmitter is determined by the provisioning of electrical drivecurrent to the appropriate DFB laser within the laser array 121 and theswitching of the appropriate MEMS switch element within the MEMS switcharray 122. As such the approach is costly in that not only must amonolithic indium phosphide (InP) M-channel DFB laser array beimplemented but also an array of M MEMS switches. Accordingly, in someinstances the free-space optical interconnect from the laser array 121to optical fiber (not depicted for clarity) is replaced by a wavelengthdivision multiplexer, such as an array waveguide grating (AWG) on thesame die as the laser array 121.

Third image 100C depicts an alternate wavelength tunable transmitterexploiting an external cavity laser (ECL) configuration wherein ratherthan the laser diode die having two high reflectivity facets to supportthe required cavity oscillation to provide gain within the semiconductordevice the laser diode die has one or no high reflectivity facets andforms a resonant optical cavity with one or two external mirrors. Inthis instance a single external mirror 131 is employed in conjunctionwith a semiconductor optical amplifier (SOA) die 132 that has a highreflectivity facet towards the optical fiber pigtail 135 and a lowreflectivity facet towards the external mirror 131. The resultant laseroutput is coupled from the SOA die 132 to the optical fiber pigtail 135via isolator 133 and lens 134. In this instance the external mirror 132is a tunable Fabry-Perot cavity filter 131 that provides for wavelengthdependent reflectivity such that the output of the assembly iswavelength specific according to the settings of the tunable Fabry-Perotcavity filter 131 allowing the emission wavelength to be adjusted.However, the characteristics of the source are now defined by thequality of the Fabry-Perot cavity filter, which even when implementedusing a MEMS construction does not achieve the sidelobe rejection of theDFB approaches.

Accordingly, it would beneficial to provide a tunable wavelengthtransmitter which can be fabricated at reduced cost commensurate withthe pricing expectations of telecom system providers and telecomoriginal equipment manufacturers (OEMs) for high volume generalizeddeployment within optical access networks, local area network, and datacenters for example. Accordingly, the inventors have established ahybrid circuit implementation exploiting an ECL configuration utilizingan InGaAsP SOA, for 1310 nm or 1550 nm wavelength ranges, in conjunctionwith selective silicon MEMS addressed wavelength reflector(s).Alternatively, other material systems such as GaAs may be employed forshorter wavelength below C-band including the S-band/E-band/O-bandoperation etc. for wavelength down from 1530 nm to 1260 nm or lower. Asdepicted in fourth image 100D in FIG. 1B the approach exploits aselective silicon MEMS addressed wavelength reflector(s) tuning elementand comprises a coupling region 144 for coupling between the SOA 145, atunable MEMS mirror 141, and an array of Bragg reflectors 143. Theoptical signals are coupled between the coupling region 144 and thearray of Bragg reflectors 143 by a planar waveguide region 142 whereinthe diverging optical signals from the Bragg reflector 143 arere-focussed by the tunable MEMS mirror 141. Accordingly, as depicted infirst and second schematics 150A and 150B the wavelength operation ofthe ECL is therefore controlled by the routing selection of the mirror141 to a selected Bragg grating within the array of Bragg reflectors143. The SOA 145 may be a Quantum Well (QW), Quantum Dot (QD) or QuantumDash (QDa) Reflective Optical Semiconductor Amplifier.

Referring to FIG. 2 an alternate configuration 200 for an ECL exploitingsilicon photonics and MEMS is depicted in first and second schematics200A and 200B respectively. Accordingly, an optical gain element 210 iscoupled via a coupling region 220 to planar waveguide region 240. Thediverging Gaussian shaped optical signal from the optical gain element210 is coupled to a selected Bragg grating within an array of Braggreflectors 250 via the planar waveguide region 240 and MEMS mirror 230wherein the design of the MEMS mirror 230 is such that the opticalsignal is coupled re-focussed to the plane of the waveguides formingpart of the Bragg gratings within the array of Bragg reflectors 250.

It would be evident that in addition to wavelength tunable transmittersthe approach of a MEMS mirror in conjunction with an array of Braggreflectors may also form part of wavelength tunable receivers,reconfigurable optical add—drop multiplexers (ROADMs), wavelengthselective optical switches, and other wavelength selective structures,for example.

OPTICAL WAVEGUIDE TECHNOLOGIES

According to embodiments of the invention exploiting MEMS mirrors, thesubstrate of choice is usually silicon due its low cost, breadth ofdoping options, and the availability of standard MEMS fabricationprocesses, prototyping facilities, and production operations, e.g. MUMPS(Multi-User MEMS Processes) from MEMSCAP, Sandia National LaboratoriesSUMMiT V processes, Teledyne DALSA's Multi-Project Wafer “Shuttle” runsand production facilities, and STMicroelectronics high volume MEMSmanufacturing facilities for example.

Silicon Nitride Core Waveguide Platform

Amongst the optical waveguide technology options that are compatiblewith deposition over SOT MEMS wafer for optical waveguides in thetelecommunication windows at 1300 nm & 1550 nm are silicon nitride(Si₃N₄) cored waveguides with silicon dioxide (SiO₂) cladding. Anexample of such a waveguide geometry is depicted in first waveguidecross-section 300A in FIG. 3 which may be employed according toembodiments of the invention. Accordingly, the optical waveguide 3000comprises a 5 μm lower silicon dioxide 330 cladding, a 70 nm siliconnitride (Si₃N₄) 340 core, and a 5 μm upper silicon dioxide 330 cladding.The waveguide cross-section 300B is depicted where the optical waveguidecouples via the air gap to the MEMS mirror (MEMSM) 3100. As the opticalwaveguide is ˜ μm thick the MEMSM 3100 at the air gap interface may bethe same material structure atop an actuated silicon (Si) MEMS structureformed within the Si substrate. The optical waveguide 3100 has below itbefore the Si substrate a layer of polyimide which is also etched backto form part of the pivot for the MEMSM 3100. Deposited onto thevertical end wall of the optical waveguide 3000 and wall of the MEMSM3100 are anti-reflection coatings.

Silicon on Insulator Waveguide Platform

Amongst the optical waveguide technology options that are compatiblewith deposition over SOT MEMS wafer for optical waveguides in thetelecommunication windows at 1300 nm 1550 nm are silicon-on-insulatorwaveguides with air cladding at the top and silicon dioxide (SiO₂)cladding at the bottom. Referring to second waveguide cross-section 300Bin FIG. 3 there is depicted a waveguide geometry 3200 according to anembodiment of the invention comprising a lower silicon dioxide (SiO₂)330 buried oxide cladding, a silicon 320 core, and relying on therefractive index of air or another material to confine total internalreflection. The waveguide cross-section 300B is similarly depicted wherethe optical waveguide 3200 couples via the air gap to the MEMSM 3300.

However, due to the high refractive index of Si the thickness limit ofthe silicon (Si) for a single-mode waveguide is 220 nm which is too thinfor MEMS devices. However, at a thickness of 1 μm modes exist within asilicon planar waveguide having modal indices of n=3.405, 3.203, 2.845,2.281, 1.487 and accordingly a rib waveguide geometry may be employed inorder to select the fundamental mode. Accordingly, the MEMSM 3300 for 1μm Si may be formed from the same material. Due to the refractiveindices the anti-reflection (AR) layer on the air gap of the opticalwaveguide 3200 and MEMSM 3300 can be formed from parylene with arefractive index of 1.66. The thickness of the AR coating would beapproximately 233 nm.

Silicon Nitride Core Waveguide Mems Circuit Designs

Referring to FIG. 4 there are depicted first to third circuits 400A,400C, and 400E respectively for MEMSM with design radii of 0.5 mm, 0.75mm, and 1.00 mm. In each instance the optical waveguides coupling to theBragg reflectors are spaced 200 μm away from the edge of the MEMSM andin each instance the distance from the pivot mounting of the MEMSM tothe optical waveguides is equal to the radius of the MEMSM. Accordingly,the resulting widths of the MEMSM in the three designs depicted in firstto third circuits 400A, 400C, and 400E respectively are 500 μm, 750 μmand 950 μm. Accordingly considering a maximum angular rotation of theMEMSM as ±3° then the lateral spacing between the upper and lower endwaveguides are 52 μm, 750 μm, and 950 μm respectively. Referring tofirst to third graphs 400B, 400D, and 400F respectively there aretherefore depicted the number of accessible channels for opticalwaveguides having spacings of 0.5 μm and 0.75 μm respectively.Accordingly, for 0.75 μm spaced waveguides the maximum number ofchannels accessible are 36 (±18 channels from centre), 54 (±27 channelsfrom centre), and 74 (±37 channels from centre) at design radii of 0.5mm, 0.75 mm, and 1.00 mm. The corresponding maximum numbers of channelsaccessible for these design radii with 0.5 μm channel spacing are 40,60, and 80 respectively.

Accordingly it would be evident that with a Si₃N₄ waveguide technologythat the number of channels can be significant and equal the number ofchannels (40) in a standard C-band 100 GHz telecommunications networkchannel plan or at 80 channels either the equivalent ITU 50 GHz C-bandchannel plan or both of the ITU C and L bands within a single device.

Silicon-On-Insulator Waveguide Mems Circuit Designs

Referring to FIG. 5 there are depicted first to third circuits 500A,500C, and 500E respectively for MEMSM with design radii of 0.5 mm, 0.75mm, and 200 mm respectively. In each instance the optical waveguidescoupling to the Bragg reflectors are spaced 200 μm away from the edge ofthe MEMSM and in each instance the distance from the pivot mounting ofthe MEMSM to the optical waveguides is equal to the radius of the MEMSM.Accordingly, the resulting widths of the MEMSM in the three designsdepicted in first to third circuits 500A, 500C, and 500E respectivelyare 160 μm, 250 μm, and 680 μm. Accordingly considering a maximumangular rotation of the MEMSM as ±3° then the lateral spacing betweenthe upper and lower end waveguides are 52 μm, 78 μm, and 209 μmrespectively. Referring to first to third graphs 1500B, 1500D, and 1500Frespectively there are therefore depicted the number of accessiblechannels for optical waveguides having spacings of 4.50 μm and 5.5 μmrespectively. Accordingly, for 5.5 μm spaced waveguides the maximumnumber of channels accessible are 16 (±8 channels from centre), 26 (±13channels from centre), and 74 (±37 channels from centre) at design radiiof 0.5 mm, 0.75mm, and 2.00 mm respectively. The corresponding maximumnumbers of channels accessible for these design radii with 4.50 μmchannel spacing are 20, 32, and 90 respectively.

Accordingly it would be evident that with a Si waveguide technology thatthe number of channels is typically lower than the number with Si₃N₄waveguide technology but that it can still be significant and equal orexceed the number of channels (40) in a standard C-band 100 GHztelecommunications network channel plan or the equivalent ITU 50 GHzC-band channel plan or both of the ITU C and L bands within a singledevice. However, generally Si tunable wavelength devices will be lowerchannel count as their footprint is smaller than the equivalent Si₃N₄circuits both in terms of the MEMSM and the footprint for the Bragggratings enabling lower costs silicon photonics applications such ascalled for by the ITU-T G.989.2 standard where the number of DWDMchannels that need to be selected is smaller than in pure WDM-PON.

Mems & Optical Waveguide Manufacturing Process Flow—Silicon Nitride Core

The manufacturing sequence described below in respect of FIGS. 6 to 9exploits standard Si manufacturing processes and Si MEMS technology inorder to fabricate the MEMSM with arrayed Bragg reflectors and opticalwaveguides. Whilst the process flow is for Si₃N₄ the process flow for Siand other optical waveguide—MEMS platforms upon silicon would be verysimilar. For the Si process flow there is clearly no requirement todeposit and pattern the SiO₂-Si₃N₄-SiO₂ waveguides whilst in others suchas silicon oxynitride, polymer, spin-on-glass, and doped SiO₂ depositionand patterning steps would be present.

Referring to first schematic 600A in FIG. 6 there is depicted a planview of a MOems-TUunable Silicon (MOTUS) optical engine comprising anSC-MEMSM mirror 620 attached to a comb drive 610 and then a Braggreflector array 640 comprising a central channel waveguide 650 whichcouples light into and out of the wavelength dependent reflector circuitand arrays of Bragg waveguides 660 disposed either side of the channelwaveguide. In other embodiments of the wavelength dependent reflectorcircuit the Bragg waveguides 660 may be disposed symmetrically eitherside of the channel waveguide, asymmetrically with different channelcounts either side of the channel waveguide, and asymmetrically to oneside of the channel waveguide. Such design considerations may be basedupon factors including, but not limited to, the angular rotation rangeof the SC-MEMSM mirror 620, the number of wavelength channels, thedesign of the MEMS comb drive 610, and the design of the electrostaticdriver circuit for the MEMS comb drive 610.

Accordingly, referring to second schematic 600B in FIG. 6 across-section of the MOTUS circuit is depicted in cross-sectional viewcomprising silicon dioxide (SiO2) 330,silicon (Si) 320, and aluminum(Al) 310 which has already been patterned and etched. Considering atypical silicon-on-insulator (SOI) substrate then the Si 320 is 5 μmthick. The Al 310 may be sputtered with a thickness of 300 nm whichafter patterning through a lithography process may be removed using astandard Al wet etch process. Subsequently in third schematic 600C theMOTUS circuit is depicted after the exposed Si 320 has been patteredlithographically and deep etched to remove 4.5 μm using a deep reactiveion etching (DRIE) process using sulphur hexafluoride (SF₆) andoctafluorocyclobutane (C₄F₈) after which the resist is stripped.

Now referring to fourth schematic 600D in FIG. 7 the optical waveguidelayer stack is deposited comprising 4 μm SiO₂ 330, 100 nm siliconnitride (Si₃N₄) 340, and 4 μm SiO₂ 330 according to another designembodiment of the Si₃N₄ waveguide platform rather than the 5 μm·SiO₂-70nm·Si₃N₄-5 μm·SiO₂ described supra in respect of FIG. 3. The depositionbeing for example through chemical vapor deposition (CVD).

Next in fifth schematic 600E in FIG. 7 the MOTUS circuit is depictedafter the optical waveguides and comb drive openings have been defined,using a DRIE etching process with a SF₆-C₄F₈-Argon (Ar) process havingan aspect ratio of 1:1:6 to etch the 4 μm SiO₂ 330-100 nm siliconnitride (Si₃N₄) 340-4 μm SiO₂ 330 stack, and the comb drive has beendefined using a DRIE etching process with a SF₆-C₄F₈ process having anaspect ratio of 1:1 to etch the 5 μm Si 320. Optionally, othermanufacturing sequences such as dual step processes employing DRIE forMEMS patterning and RIE processing for optical waveguide structures maybe employed to provide reduced sidewall roughness and Teflon freeprocessing.

Subsequently in sixth schematic 600F in FIG. 7 the MOTUS circuitcross-section is depicted after the air gap has been formed and theexcess regions of the optical waveguides atop the comb drive etc. havebeen removed. These steps are achieved using a DRIE etching process witha SF₆-C₄F₈ Argon (Ar) process having an aspect ratio of 1:8 to etch theSiO₂ 330-Si₃N₄ 340-SiO₂ 330 stack, and the comb drive has been definedusing a DRIE etching process with a SF₆-C₄F₈ having an aspect ratio of2:1 to etch the 0.5 μm Si 320. Whereas the preceding steps were carriedout with a critical dimension of approximately 5 μm the photolithographyfor the air gap processes have a critical dimension of approximately 1μm. Next in seventh schematic 600G in FIG. 8 the Bragg grating sectionsof the optical Bragg reflectors are photolithographically defined andetched using a DRIE etching process with a SF₆-C₄F₈-Argon (Ar) processhaving an aspect ratio of 1:8 to partially etch the upper claddingcomprising SiO₂ 330.

Alternatively, the process sequence resulting in fifth and sixthschematics 600E and 600F may be reversed such that the waveguide isfirst removed above the MEMS actuator part and then it would bepatterned using a more optimized mask. Now referring to eighth schematic600H in FIG. 8 a reflective layer, gold (Au) 380, is deposited andpatterned onto the SC-MEMSM mirror sidewalls and anti-reflection (AR)coatings are deposited and patterned onto the SC-MEMSM mirror sidewalland optical waveguide sidewall either side of the air gap. The ARcoating may be magnesium fluoride, MgF₂,for example with a thickness of280 nm. Subsequently as depicted in ninth schematic 600I the frontsurface of the MOTUS circuit is protected for wafer backside processingsteps that follow. Accordingly, polyimide 350 with a thickness of 5 μmmay be spin-coated onto the wafer and cured, e.g. 300° C. for 2 hours.Optionally at this point the substrate may also be thinned usingChemical Mechanical Polishing (CMP) for example. Polyimide 350 may,optionally, be photoresist rather than polyimide.

In ninth schematic 600I in FIG. 9 the substrate, e.g. silicon, islithographically processed to define the trench below the MEMS combdrive and SC-MEMSM mirror sections of the MOTUS circuit. This may, forexample, be via a DRIE using SF₆-C₄F₈ stopping at the SiO₂ 320 layer.Then in tenth schematic 600J the SiO₂ 320 is etched from the backsideusing ME process, for example, followed by resist stripping, waferdicing, polyimide removal by plasma ashing, for example, and mechanicalpolishing of the MOTUS circuit die sidewall for connection between thechannel waveguide and optical fiber.

Semi-Circular Mems Mirror (Sc-Memsm) & Actuator Design

As discussed supra in respect of the MOTUS an optical signal is coupledfrom an initial optical waveguide to a MEMS mirror wherein it isreflected and coupled to a subsequent optical waveguide having a Bragggrating formed within. The reflected optical signals from the Bragggrating then traverse the reverse path. Accordingly, the MEMS mirrorrotates to couple to different optical waveguides with different Bragggratings and thence provide the required wavelength tunability. In orderto minimize losses, the optical signal is maintained in waveguides allthe way through this process and accordingly the region between the endsof the waveguides and the mirror is a waveguide as well. This results ina semi-circular MEMS mirror (SC-MEMSM) so that the mirror can rotate,the optical signal is maintained within the waveguide, and the waveguidecan rotate relative to the channel waveguide section of the MOTUSoptical engine.

Accordingly, referring to FIG. 10A and first to third images 1010 to1030 respectively there is depicted a semi-circular MEMS mirror(SC-MEMSM) design according to an embodiment of the invention exploitingelectrostatic actuation with slanted fingers. Accordingly, as designedthe SC-MEMSM will rotate when the 8 μm SC-MEMSM fingers areelectrostatically attracted to the drive contacts. The SC-MEMSM fingeradjacent the solid V_(DD) electrode is angled at 4.5° whilst the otherSC-MEMSM fingers adjacent V_(DD) electrode fingers are angled at 6°. Thedisc of the SC-MEMSM subtends an arc of 135° and is attached via a 3 μmpivot element to the V_(SS) electrode. Towards the end of the solidV_(DD) electrode by the SC-MEMSM finger a stopper electrode is providedwhich is selectively biased to V_(SS).

Referring to fourth to sixth images 1040 to 1060 respectively in FIG.10B there is depicted a semi-circular MEMS mirror (SC-MEMSM) designaccording to an embodiment of the invention exploiting electrostaticactuation with a comb drive and slanted fingers. Accordingly, asdesigned the SC-MEMSM will rotate when the 11 μm SC-MEMSM fingers withinthe comb drive are electrostatically attracted to the drive contacts.The SC-MEMSM also comprises a SC-MEMSM finger adjacent the solid V_(DD)electrode is angled at 4.5° whilst the SC-MEMSM comb drive fingers thatrotate are angled at 6° where these are attracted towards the other combdrive fingers (right-hand side) and are not angled where these will berepelled away from the other comb drive fingers (left-hand side). Thedisc of the SC-MEMSM subtends an arc of 135° and is attached via a 3 μmpivot element to the V_(SS) electrode. Towards the end of the solidV_(DD) electrode by the 8 μm SC-MEMSM finger a stopper electrode isprovided which is selectively biased to V_(SS).

SC-MEMSM Mirror Design

Within the embodiments of the invention, process flows, and variantsdiscussed and described supra in respect of FIGS. 1 to 10 it would beevident to one skilled in the art that whilst SC-MEMSM designs featurethroughout that there are two different classes of SC-MEMSM within thesefigures that each share a semicircular disk rotating with a small airgap adjacent to a curved planar waveguide structure. However, the rearreflecting mirror surface of the SC-MEMSM differs in the two classes.

The first class is where the rear reflecting mirror surface is a planarmirror such that the optical signals impinging upon it at an angle β° tothe normal of the planar surface are reflect and propagate away at anangle β° on the other side of the normal. Such a rear reflecting planarmirror is depicted in the SEM images in FIG. 10. Accordingly, acollimated optical signal will reflect and maintain collimation whilst adiverging beam with reflect and still diverge.

The second is a curved back mirror where the reflecting mirror surfacehas a predetermined profile such that the normal to the mirror surfacevaries across the surface and hence whilst locally each optical signalwill reflect according to the normal at its point of incidence theoverall effect of the mirror on beam is determined by the profile of themirror and the point at which the optical beam impinges. Considering therear reflecting planar mirror as depicted in FIGS. 1 (100D), 2, 4-6, and9 the surface is concave with respect to the impinging optical beamwhich is aligned to the axis of the curved mirror surface. As a resultthe concave rear reflecting mirror results in focusing of a divergingbeam such that where the radius of curvature of the rear surface equalsits distance from the source of a diverging optical beam it will refocusthe beam back at the same distance but rotationally offset according tothe rotation angle of the SC-MEMSM. Hence, for example the MOTUSdepicted in third schematic 500E in FIG. 5 has a radius of curvature forthe rear reflecting surface of the SC-MEMSM of 2000 μm with the pivotpoint 2000 μm from the central channel waveguide. The front surface ofthe SC-MEMSM is the curved surface of radius 1,800 μm. In contrast isfirst schematic 500A in FIG. 5 the radius of curvature of the rearreflecting surface is 500 μm whilst the front surface of the SC-MEMSM isthe curved surface of radius 300 μm.

However, it would be evident that other profiles for the rear reflectingmirror surface may be employed according to the functionality of theoverall optical circuit and the characteristics of the mirror required.For example, the rear surface may have a radius of curvature lower thanthe distance from the waveguides such that the optical signals arefocused within the body of the SC-MEMSM and are diverging at the planeof the optical waveguides.

Referring to FIG. 11A there is depicted a schematic of a first MOTUSoptical engine 1100 which comprises an input/output waveguide 1170 thatcouples to the semi-circular MEMS mirror (SC-MEMSM) 1140 via a planarwaveguide 1190 and air gap 1150. According, the optical signal from theinput/output waveguide 1170 is reflected and coupled to one of thedistributed Bragg reflectors (DBRs) within its associated Braggwaveguide 1160. The optical signals reflected from the selected DBR arethen guided back via its associated Bragg waveguide 1160, through theplanar waveguide 1190 and SC-MEMSM 1140 before being reflected againback towards the input/output waveguide 1170. Accordingly, a widebandoptical signal is filtered by the appropriately selected DBR within itsBragg waveguide 1160 or a cavity formed comprising the selected DBRwithin the Bragg waveguide 1160 and an external optical gain medium witha broadband reflector may become a wavelength settable laser source. TheSC-MEMSM 1140 is anchored at MEMS anchor 1120 and driven through rotaryelectrostatic actuator 1110 such that the SC-MEMSM rotates to therequired angle to couple optical signals from the input/output waveguide1170 to the desired Bragg waveguide 1160. Optionally the planarwaveguide 1190 may be similarly curved and of finite width.

Beneficially, the small planar region with a larger optical mode makesthe insertion loss of the MOTUS optical engine 1100 less sensitive toedge roughness. Referring to FIG. 11B there is depicted a variant 1150of the first MOTUS optical engine 1100 wherein the planar waveguide 1190is absent and the Bragg waveguides 1160 and input/output waveguide 1170terminate within this close to the air gap 1150. Optionally in otherdesigns no planar waveguide 1190 is provided and the Bragg waveguides1160 may terminate at the air gap 1150 or a predetermined distance fromthe air gap 1150. Whilst not evident in these schematics the Braggwaveguides 1160 may be angled at their junction with the planarwaveguide 1190 or air gap 1150 to align the waveguide axis with theincident optical beam. Optionally, the number of gratings either side ofthe input/output waveguide 1170 may be equal, unequal, of one gratingpassband characteristic, of multiple passband characteristics (e.g. acombination of 50 GHz+100 GHz, 100 GHz+200 GHz, or 100 GHz+CWDM ITUpassband profiles).

Referring to FIG. 12A there is depicted a schematic of a second MOTUSoptical engine 1200 which comprises an input/output waveguide 1220 thatcouples to the semi-circular MEMS mirror (SC-MEMSM) 1140 via a lens1210, a planar waveguide 1190 and air gap 1150. According, the opticalsignal from the input/output waveguide 1220 is reflected and coupled toone of the distributed Bragg reflectors (DBRs) within its associatedBragg waveguide 1160. The optical signals reflected from the selectedDBR are then guided back via its associated Bragg waveguide 1160,through the planar waveguide 1190 and SC-MEMSM 1140 before beingreflected again back towards the input/output waveguide 1220.Accordingly, a wideband optical signal is filtered by the appropriatelyselected DBR within its Bragg waveguide 1160 or a cavity formedcomprising the selected DBR within the Bragg waveguide 1160 and anexternal optical gain medium with a broadband reflector may become awavelength settable laser source. The SC-MEMSM 1140 is anchored at MEMSanchor 1120 and driven through rotary electrostatic actuator 1110 suchthat the SC-MEMSM rotates to the required angle to couple opticalsignals from the input/output waveguide 1220 to the desired Braggwaveguide 1160. Optionally the planar waveguide 1190 may be similarlycurved and of finite width. Beneficially, the small planar region with alarger optical mode makes the insertion loss of the MOTUS optical engine1100 less sensitive to edge roughness.

In contrast to the first MOTUS optical engine 1100 the second MOTUSoptical engine 1200 optical signals coupled from the input/outputwaveguide 1220 to the Bragg grating within a Bragg waveguide 1160 thatare not reflected propagate further within the Bragg waveguide 1160until they couple to lens 1210 and are focussed onto through waveguide1230. Accordingly, if, for example 40 channels of 100 GHz spaced C-band(e.g. ITU channels 21-60) are coupled to the second MOTUS optical engine1200 and a Bragg waveguide is designed to reflect a sub-band comprisingchannels 21-24 then the remaining channels 25-60 will be coupled throughthe Bragg grating unaffected into the lens 1210 and thence to thethrough waveguide 1230.

Referring to FIG. 12B there is depicted a variant 1250 of the secondMOTUS optical engine 1200 wherein the planar waveguide 1190 is absentand the Bragg waveguides 1160 and input/output waveguide 1170 terminatewithin this close to the air gap 1150. Optionally in other designs noplanar waveguide 1190 is provided and the Bragg waveguides 1160 mayterminate at the air gap 1150 or a predetermined distance from the airgap 1150. Whilst not evident in these schematics the Bragg waveguides1160 may be angled at their junction with the planar waveguide 1190 orair gap 1150 to align the waveguide axis with the incident optical beam.Optionally, the number of gratings either side of the input/outputwaveguide 1170 may be equal, unequal, of one grating passbandcharacteristic, of multiple passband characteristics (e.g. a combinationof 50 GHz+100 GHz, 100 GHz+200 GHz, or 100 GHz+CWDM ITU passbandprofiles).

Now referring to FIG. 13 there is depicted a schematic of what theinventors refer to as a Reconfigurable Optical Add/Drop Signal andElectronically Regenerated (ROADSTER), a tunable add-drop module.Accordingly, the schematic depicts a 4-channel ROADSTER exploiting firstand second MOTUS optical engines 1100 and 1150 respectively. As such theROADSTER provides for the extraction of 4 wavelengths, in thisembodiment, of a predefined sub-band and reinsertion of the samewavelengths with newly generated signals on the optical medium. When thefull optical band signals are received at the ROADSTER (Rx) at Rx Inport 1300B the signals are coupled initially to a MOTUS basedReconfigurable Band DMUX 1350 via a circulator 13030. The ReconfigurableBand DMUX 1350 tunes to a selectable sub-band filter and accomplishestwo distinct operations. First, the selected sub-band is dropped andsecondly, the remaining channels are coupled to 2:1 MUX 1380 and thereinrecoupled to the network via Tx Out port 1300A. The selected sub-band isthen coupled to a Channel DMUX 1355 wherein the discrete wavelengths inthe sub-band are separated and coupled to 4 photodetectors (PDs) devicesthus extracting the modulated optical signals into an electricalquadruple communication port programming interface (CPPI-4) at the hostlevel within controller 1390. The non-selected sub-bands are opticallyamplified with Optical Amplifier 1385 before re-launch into the opticalnetwork. Accordingly, Reconfigurable Band DMUX 1350 exploits a secondMOTUS optical engine such as described in respect of FIGS. 12A and 12Band represented here by second MOTUS optical engine 1200.

Channel DMUX 1355 may be formed from grating assisted directionalcouplers in order to provide the required separation of the reflectedoptical signals from the transmitted optical signals. Alternatively,rather than 4 filters the channel DMUX 1355 may employ 3 seriallyconnected filters and simply couple the output of the third filter tothe last photodetector. Alternatively, channel DMUX 1355 may comprise 3sets of 10 Bragg gratings configured in a 1-skip-3 configuration anddaisy chained through 4 optical circulators and connected to the 4photodiodes.

Also depicted are four MOTUS based Lambda Tunable transmitters Tx1 1310to Lambda Tunable transmitter Tx4 1340 respectively which are used togenerate the new optical signals within the dropped sub-band forre-insertion into the network. The electrical CPPI-4 sub-band signalfrom a host is modulated to the right wavelengths on each MOTUS basedLambda Tunable transmitters Tx1 1310 to Lambda Tunable transmitter Tx41340 respectively. Each of the Lambda Tunable transmitters Tx1 1310 toLambda Tunable transmitter Tx4 1340 respectively has 10 programmablewavelengths of operation such that the 10 sub-bands are supported by theappropriate selection of the distributed Bragg reflector (DBR), e.g.Bragg grating, within the MOTUS optical engine. Accordingly, theActuator Driver Circuit 1395 aligns the silicon MEMS mirrors within thefour transmitting MOTUS optical engines to the desired sub-band.Accordingly, the tunable source comprising either a wideband laser incombination with the MOTUS optical engine or an optical gain blockwithin a resonant cavity with the MOTUS optical engine provides theappropriate wavelength from the selected sub-band which is then coupledto an external modulator within each of the Lambda Tunable transmittersTx1 1310 to Lambda Tunable transmitter Tx4 1340 respectively. Theoptical signals are then coupled to 4:1 MUX 1370 such that at this stagethe four newly generated signals are combined together and then in 2:1MUX 1380 are coupled to the remaining passed-through sub-bands.

Accordingly, Lambda Tunable transmitters Tx1 1310 to Lambda Tunabletransmitter Tx4 1340 respectively which exploit the first MOTUS opticalengine 1100 in conjunction with an optical gain element 13010 andexternal modulator 13020. Any optical amplification within the ROADSTER600 has been omitted for clarity. As depicted the Channel DMUX 655 is anarray of Bragg grating devices, such as grating assisted reflectivedirectional couplers or grating assisted transmissive directionalcouplers for example in order to remove the requirement for isolators toseparate reflected optical signals from the forward propagating signals.The Bragg grating devices may be cyclic, low free spectral range,geometries such that one Channel DMUX 655 operates on all bands.

Motus Semiconductor Integration

As discussed supra in respect of embodiments of the invention the MOTUSoptical engine has been described as forming part of a tunable opticalsource in conjunction within an optical gain medium. If a semiconductoroptical gain block is provided having one facet with low reflectivityand another facet with high reflectivity then if the facet with lowreflectivity is coupled via the MOTUS optical engine to a wavelengthselective reflector then the resulting wavelength dependent opticalcavity will oscillate and lase at the wavelength defined by thewavelength selective reflector. With a MOTUS optical engine theresulting laser will be programmable in wavelength according to each ofthe Bragg reflectors selected through the SC-MEMSM.

As the MOTUS optical engine is based upon MEMS devices exploitingsilicon on insulator substrates within the embodiments of the inventiondescribed supra then it would be evident that the semiconductor opticalgain block may be integrated onto the MOTUS optical engine. Referring toFIG. 14 there are depicted first and second schematics for theintegration of a semiconductor optical gain block with a MOTUS opticalengine 1430 exploiting a SiO₂-Si₃N₄-SiO₂ waveguide upon asilicon-on-insulator (SOI) substrate.

In first schematic 1400 a gain block 1410, which typically comprises anInGaAsP stack upon an InP substrate which is etched to form a rib orrib-loaded waveguide, has deposited upon it alignment features which keyto features etched into the silicon underlying the SiO₂-Si₃N₄-SiO₂waveguide. Accordingly, the position of the gain block 1410 is laterallydefined by the features etched into the silicon which may be provided aspart of the same processing sequence as the formation of the MOTUSoptical engine. The vertical position of the gain block 1410 relative tothe SiO₂-Si₃N₄-SiO₂ waveguide is determined by the features etched intothe silicon, the alignment features deposited onto the gain block 1410,and the tolerances of the SiO₂-Si₃N₄-SiO₂ waveguide layers.

In second schematic 1450 a gain block 1420 is aligned to an opticalwaveguide formed within a SiO₂-Si₃N₄-SiO₂ waveguide. In this instance,the vertical alignment of the optical waveguide within the gain block1420 to the SiO₂-Si₃N₄-SiO₂ waveguide is determined by the depth of theInP substrate etching of the gain block 1420 and the SiO₂-Si₃N₄-SiO₂waveguide tolerances whilst lateral alignment is achieved throughphysical features formed within the SiO₂-Si₃N₄-SiO₂ structure and thegain block 1420 but now these are solely for lateral alignment.

Now referring to FIG. 15A there are depicted first and second schematics1500A and 1550A for the integration of a semiconductor optical gainblock with a MOTUS optical engine 1530 exploiting a Si waveguide upon asilicon-on-insulator (SOI) substrate with a SOI waveguide rather than aSiO₂-Si₃N₄-SiO₂ waveguide. In first schematic 1500A a gain block 1510,which typically comprises an InGaAsP stack upon an InP substrate whichis etched to form a rib or rib-loaded waveguide, has deposited upon itsalignment features which key to features etched into the silicon layerwhich also forms the optical waveguide. Accordingly, the position of thegain block 1510 is laterally defined by the features etched into thesilicon which may be provided as part of the same processing sequence asthe formation of the MOTUS optical engine. The vertical position of thegain block 1510 relative to the optical waveguide is determined by thefeatures etched into the silicon, the alignment features deposited ontothe gain block 1510, and the tolerance of the Si waveguide layers.

In second schematic 1550A a gain block 1520 is aligned to an opticalwaveguide formed within a Si waveguide. In this instance, the verticalalignment of the optical waveguide within the gain block 1420 to the Siwaveguide is determined by the depth of the InP substrate etching of thegain block 1420 and the etch depth, Si waveguide tolerances whilstlateral alignment is achieved through physical features formed withinthe Si layer and the gain block 1420 but now these are solely forlateral alignment.

Referring to FIG. 15B there are depicted first and second cross-sections1500B and 1550B respectively through wavelength selective MOTUS opticalengines according to an embodiment of the invention with hybrid buttcoupling assembly of a semiconductor optical gain block 1520B withsilicon nitride cored MOTUS 1430 and silicon cored MOTUS 1530respectively. Accordingly, as depicted in each of first and secondcross-sections 1500B and 1550B respectively the semiconductor opticalgain block 1520B is aligned vertically, laterally, and longitudinally tothe appropriate common waveguide with each of the silicon nitride coredMOTUS 1430 and silicon cored MOTUS 1530 respectively. As depicted ineach anti-reflection (AR) coatings 1540A/1545A and 1540B/1545B areapplied to the MOTUS and the semiconductor optical gain block 1520Brespectively. These AR coatings may be established assuming a small airinterface within the transition region or no air gap. Alternatively, asingle coating may be applied to one or other of the MOTUS andsemiconductor optical gain block assuming no air gap. Optionally, thesemiconductor optical gain block 1520B may be mounted to a separateelement of an overall assembly or it may be mounted to an underlyingsilicon substrate that has been appropriately patterned and deep etchedfor placement of the semiconductor optical gain block.

The optical interface between the semiconductor optical gain block 1520Band the silicon nitride cored MOTUS 1430 and silicon cored MOTUS 1530respectively may also comprise angled facets relative to the opticalwaveguides with each of the semiconductor optical gain block 1520B andthe silicon nitride cored MOTUS 1430 and silicon cored MOTUS 1530respectively. Alternatively, the facets may be normal, and thewaveguides angled relative to the facets. The angled interfaces mayreduce the reflectance and/or increase the AR coating manufacturingtolerances.

In addition to the optical gain block an external modulator may also behybridly integrated with the MOTUS optical engine either as a discreteelement or integrated with the optical gain block. It would also beevident that whilst the optical gain block is shown at the end of theMOTUS optical engine distal from the SC-MEMSM that in other embodimentsof the invention according to the number of channels, rotation angle ofthe SC-MEMSM, acceptable handling width of optical gain block, etc.,that the gain block 1610 discretely or the gain block 1610 and modulator1620 may be disposed closer to the SC-MEMSM thereby reducing the lengthof the optical cavity forming the laser cavity as depicted in FIG. 16.

Accordingly, referring to FIG. 17 there is depicted analysis of themaximum modulation speed of a cavity comprising a facet of a gain blockand a Bragg reflector versus the length of the cavity. Accordingly, forOC-48 data transmission at 2.5 Gb/s the cavity length with a Si₃N₄ coredwaveguide should be less than approximately 4 mm compared to 2.5 mm forSi With increasing speed the cavity length decreases to the point thatat OC-192 (10 Gbps) cavity lengths should be less than 1 mm.

Referring to FIG. 18 there is depicted a wavelength selective MOTUSoptical engine 1800 according to an embodiment of the invention withhybrid integration of a semiconductor die 1840 which comprisesmonolithically integrated form a semiconductor optical gain block 1830,a high reflectivity mirror 1820, and external Mach-Zehnder modulator1810 such that the multiple distributed Bragg reflector—external tunablecavity laser (MDBR-ECTL) is externally modulated by the Mach-Zehndermodulator 1810. The high reflectivity mirror 1820 operates inconjunction with the wavelength selective Bragg grating within the MOTUSoptical engine to provide the required cavity for lasing operation inconjunction with the semiconductor optical gain block 1830.

Now referring to FIG. 19 there is depicted a wavelength selective MOTUSoptical engine according to an embodiment of the invention withpost-wavelength filter optical detectors 1920 at the ends of the opticalchannel waveguides within which the Bragg gratings are formed. Eachoptical detector 1920 is coupled to the circuit edge via a track 1910.Accordingly, the optical power detected by an optical detector 1920 maybe employed to provide feedback control for the semiconductor opticalgain block within the laser structure. This is possible as the Bragggrating is not 100% reflective and accordingly some of the laser signalreaches the optical detector 1920 and as the laser oscillates at thewavelength of the Bragg grating the power detected on that channeldetector 1920 is proportional to the laser output. Additionally, opticalpower comparison between the optical detector 1920 for the selectedwavelength and those channels adjacent may be employed to provideadditional feedback information.

Referring to FIG. 20 there is depicted a wavelength selective MOTUS 2050optical engine according to an embodiment of the invention acting as thetuning element for a wavelength selective receiver 2000. Accordingly, aninput optical signal is coupled to an optical circulator 2010 wherein itis coupled to the MOTUS 2050. The reflected signal at the wavelengthselected by tuning the SC-MEMSM within the MOTUS 2050 is then coupledback to the optical circulator 2010 and therein to the photodetector2020.

Whilst the optical circulator 2010 provides for separation of the inputforward propagating signals and backward propagating signals these canbe bulky and expensive devices. Accordingly, referring to FIG. 21 thereis depicted a wavelength selective receiver (WSR) 2100 according to anembodiment of the invention exploiting a wavelength selective MOTUSoptical engine with Bragg grating based transmissive Fabry-Perot filtersand coupler combiners. Accordingly, the SC-MEMSM mirror allows forselection of the appropriate Fabry-Perot filter 2140 within the array ofFabry-Perot filters. Each Fabry-Perot filter 2140 is comprised of firstand second Bragg gratings 2130A and 2130B that act in conjunction withone another to provide a high finesse filter, see for example Legoubinet al in “Free Spectral Range Variations in Grating-Based Fabry-PerotFilters Photowritten in Optical Fibers” (J. Opt. Soc. Am. A, Vol. 12,No. 8, pp-1687-1694). The outputs of the upper and lower waveguidegroups are each coupled to a multi-mode interferometer (MMI), first andsecond MMI 2110A and 2110B respectively, and therein to first and secondphotodetectors 2120A and 2120B. Optionally, directional couplers and/orMach-Zehnder interferometers may be cascaded to provide similarfunctionality.

As noted supra the design of the MOTUS optical engine allows forasymmetry in the waveguides. An example of this is depicted in FIG. 22where there is depicted a WSR 2200 according to an embodiment of theinvention exploiting a wavelength selective MOTUS optical engine withBragg grating based transmissive Fabry-Perot filter array and offsetinput waveguide. Accordingly, as in FIG. 21 each waveguide comprises aFabry-Perot filter 2140 is comprised of first and second Bragg gratings2130A and 2130B that act in conjunction with one another to provide ahigh finesse filter. Now, however, the outputs of these are coupled viaa single MMI 2210 to a single photodetector 2220.

Now referring to FIG. 23 there are depicted first and secondcross-sections X-X and Y-Y through a wavelength selective opticaltransmitter according to an embodiment of the invention incorporatingintegrated semiconductor structure 2350 comprising a semiconductoroptical gain block 2330, high reflectivity mirror 2320, and externalMach-Zehnder modulator 2310. Second cross-section Y-Y is similar to thatdepicted in eleventh image 600K in FIG. 9 for a finished MOTUS opticalengine depicted the cross-section through the SC-MEMS and Braggwaveguide grating. As depicted in first cross-section X-X according tothis embodiment of the invention the semiconductor structure 2350 hasbeen deposited directly onto the silicon substrate of thesilicon-on-insulator structure such the waveguide sections of thesemiconductor structure 2350 are butt-coupled to the silicon corewaveguides of the MOTUS optical engine. Whilst these interfaces aredepicted as being perpendicular within FIG. 23 these interfaces may beangled to suppress return loss as in fact they may also be in the otherembodiments of the invention in FIGS. 14 and 15 for example whereinhybrid flip-chip integration is depicted. According to the operatingwavelength of the MOTUS the semiconductor structures may be AlGaInAs,InGaAsP, and GaAs based for example.

Within other embodiments of the invention according to variations offlip-chip mounting the semiconductor optical gain block and externalmodulator evanescent coupling from the passive waveguides, see forexample Park et al. in “A Hybrid AlGaInAs Silicon Evanescent Amplifier”(IEEE Phot. Tech. Lett., Vol. 19, pp.230-232) and Bowers et al. in“Integrated Optical Amplifiers on Silicon Waveguides” (Proc. IntegratedPhotonics and Nanophotonics Research and Applications, Paper ITuG1,2007).

Within other embodiments of the invention the semiconductor opticallaser may be formed within the silicon core waveguides using conceptsincluding, but not limited to, microring lasers. At other wavelengthranges, e.g. 1300 nm, structures such as semiconductor componentscomprising a Si substrate, an active region, and a Si capping layer onsaid active region. The active region, see U.S. Pat. No. 6,403,975, maybe a superlattice comprising alternating layers of Si(1-y)C(y) andSi(1-x-y)Ge(x)C(y). In another embodiment it is a superlatticecomprising a plurality of periods of a three-layer structure comprisingSi, Si(1-y)C(y) and Si(1-x)Ge(x) and in another a plurality of periodsof a three-layer structure comprising Si, Si(1-y)C(y) andSi(1-x-y)Ge(x)C(y) layers.

Within the embodiments of the invention a conventional semiconductorgain block based upon a semiconductor optical amplifier (SOA) may beemployed for the gain block. Alternatively, a quantum dot SOA (QD-SOA)may be employed with appropriate coatings to provide the gain block oras an optical amplifier within optical circuits such as the ROADSTER forexample. In some embodiments of the invention a pair of QD-SOAamplifiers may be employed rotated with respect to one another by 90° inorder to compensate for polarization dependent effects within theQD-SOAs. Alternatively, a polarization diversity circuit with dualoptical amplifiers may be employed.

Now referring to FIGS. 24A to 26 there are depicted micro-positionerconcepts according to embodiments of the invention as established by theinventors in U.S. Provisional Patent Application 62/037,655 “Methods andSystems for Microelectromechanical Packaging” filed Aug. 15, 2014, theentire contents of which are herein included by reference. Accordingly,in FIG. 13A there is depicted a cross-section of the waveguide/MEMSstructure of an optical component exploiting MEMS such as a MOTUS asdescribed supra in respect of embodiments of the invention wherein inaddition to MEMS mirror a MEMS micro-actuator is implemented foractive/dynamic alignment. Accordingly, a silicon 320 substrate ofnominal thickness 675 μm has formed upon it a 1-3 μm layer of SiO₂ 330and then a silicon 320 layer of minimum thickness 11-16 μm dependingupon the optical waveguide structure which forms the basis of the MEMSelements. Within the waveguide region(s) the waveguide is comprised of alower cladding layer of SiO₂ 330 with thickness 2-4 μm, a siliconnitride (Si₃N₄) core of thickness 70 nm≤t≤220 nm, and upper claddinglayer of SiO₂ 330 with thickness 2-4 μm. Accordingly, based upon theetching of the lower 1-3 μm layer of SiO₂ 330 and silicon 320 substratedifferent regions of the device may be formed including supported MEMSstructure 2410, free standing MEMS structure 2420,Micro-Opto-Electro-Mechanical structure 2430, and optical waveguidestructure 2440.

Within other embodiments of the invention different Si₃N₄ waveguide corethicknesses may be employed according to the design criteria of theMOTUS. For example, at 1550 nm in singlemode optical waveguides reducedpolarization dependence can be achieved through the use of squarewaveguides with SiO₂ upper and lower cladding. For example, a 600 nm×600nm core may be employed.

Now referring to FIG. 24B there is depicted a cross-section of a MOEMSexploiting a waveguide/MEMS structure similar to that depicted in FIG.24A and of an optical component exploiting MEMS such as a MOTUS asdescribed supra in respect of embodiments of the invention wherein inaddition to MEMS mirror a MEMS micro-actuator is implemented foractive/dynamic alignment. As with FIG. 24A the layer stack comprises asilicon 320 substrate of nominal thickness 675 μm has formed upon it a1-3 μm layer of SiO2 330 and then a silicon 320 layer of minimumthickness 11-16 μm depending upon the optical waveguide structure whichforms the basis of the MEMS elements was originally formed but has beenetched down to 7-8 μm. The optical waveguide structure is comprised of alower cladding layer of SiO₂ of 330 with thickness 2-4 μm, a siliconnitride (Si₃N₄) core of thickness 70 nm≤t≤220 nm, and upper claddinglayer of SiO₂ 330 with thickness 2-4 μm. Accordingly, the MOEMS isstructured with 4 different cross-sections including supported MOEMS2450, unsupported MOEMS 2460, exposed core 2470, and optical waveguidestructure 2440. In unsupported MOEMS 2460 the underlying silicon 320substrate and silicon dioxide 330 have been removed, except foranchor(s) 2470, leaving the optical waveguide supported on the MEMSsilicon 320. In exposed core 2470 the underlying silicon 320 substrate,sacrificial silicon dioxide 330, MEMS silicon 320, and upper/lowersilicon dioxide 330 claddings have been removed leaving a short regionof exposed silicon nitride 240 core. Within other embodiments of theinvention exposed core 2470 may be alternatively be the opticalwaveguide absent MEMS silicon 320 support or the optical waveguide withreduced thickness upper and/or lower cladding.

Now referring to FIG. 24C there is depicted a cross-section of a MOEMSexploiting a waveguide/MEMS structure similar to that depicted in FIGS.24A and 24B comprising a silicon 320 substrate of nominal thickness 675μm; a 1-3 μm layer of SiO2 330; a silicon 320 mechanical layer; and anoptical waveguide structure comprised of a lower cladding layer of SiO₂330 with thickness 2-4 μm , a silicon nitride (Si₃N₄) core of thickness70 nm≤t≤220 nm, and upper cladding layer of SiO₂ 330 with thickness 2-4μm. In this instance the unsupported MOEMS 2460 is replaced withreleased MOEMS 2490 wherein the mechanical silicon 320 layer has beenreleased from the silicon 320 substrate by etching the lowermost SiO2330 but the silicon 320 substrate has not been removed. Accordingly, theanchors 2480 have now been replaced with anchors 2495 formed solelywithin the sacrificial SiO2 330 layer.

Now referring to FIG. 25 there is depicted a MOEMS optical waveguidemicro-positioner (MOEMS OWMP) 2500A according to an embodiment of theinvention together with first and second variant MOEMS OWMPs 2500B and2500C respectively. As depicted the MOEMS OWMP 2500A comprises thefollowing regions:

-   -   an initial section upon non-suspended waveguide 2510, equivalent        to optical waveguide structure 2410;    -   a first exposed core region 2520, equivalent to exposed core        2470;    -   optical waveguide upon actuator 2530, equivalent to unsupported        MOEMS 2460; and    -   a second exposed core region 2540, equivalent to exposed core        2470.

As depicted the optical waveguide upon actuator 2530 is supported byMEMS beam 2550 which is connected to MEMS actuator 2560. Accordingly,motion of the MEMS actuator 2560 results in translation of the opticalwaveguide upon actuator 2530 and second exposed core region 2540relative to either another optical waveguide or an optical component. Assuch, with a pair of optical waveguides of which the MOEMS OWMP 2500Aforms part then a variable optical attenuator (VOA) functionality can bedirectly integrated into the MOEMS for power management etc. First andsecond variant MOEMS OWMPs 2500B and 2500C respectively depict designswithout the second exposed core region 2540 and with an opticalwaveguide taper respectively. Other variants such as an opticalwaveguide taper forming part of the second exposed core region 2540 maybe implemented, for example, as would be evident to one of skill in theart.

Now referring to FIG. 26 there is depicted a MOEMS optical waveguidemicro-positioner according to an embodiment of the invention in firstposition 2600 and second position 2650. As depicted first and secondactuators 2630A and 2630B are coupled at one end to first and secondangular comb drives 2670A and 2670B respectively. At the other ends uponthe first and second actuators 2630A and 2630B are optical waveguide2620 sections. As evident from FIG. 26 and inset 2600 the opticalwaveguide 2620 comprises:

-   -   an initial section upon non-suspended waveguide 2610, equivalent        to supported MOEMS 2450;    -   a first exposed core region, equivalent to exposed core 2470;    -   optical waveguide upon second actuator 2630B, equivalent to        unsupported MOEMS 2460;    -   a second exposed core region, equivalent to exposed core 2470;    -   optical waveguide upon first actuator 2630A, equivalent to        unsupported MOEMS 2460; and    -   a third exposed core region, equivalent to exposed core 2470 and        the portion of the optical waveguide 2620 closest to the optical        gain block die 2660.

Accordingly, activation of one or other or both of the first and secondangular comb drives 2670A and 2670B results in the movement of therespective one of the first and second actuators 2630A and 2630B whichpivot about their respective anchors 2640A and 2640B such that thedistal ends of the first and second actuators 2630A and 2630B from thefirst and second angular comb drives 2670A and 2670B similarly movethereby moving the optical waveguide supported by these distal ends ofthe first and second actuators 2630A and 2630B. In FIG. 26 in firstconfiguration 2600 and inset 2600A the MOEMS optical waveguidemicro-positioner is depicted in a first state, e.g. as manufactured oralternatively as the first and second angular comb drives 2670A and2670B have been driven to position the first and second actuators 2630Aand 2630B to these positions. Now referring to second configuration 2650and second inset 2600B then the MOEMS OWMP according to an embodiment ofthe invention is depicted after rotation and/or further rotation of thefirst and second angular comb drives 2670C and 2670D which result in thepivoting of the distal ends of the first and second actuators 2630A and2630B around first and second anchors 2640A and 2640B which result inthe optical waveguide geometry being varied to that of suspendedwaveguide 2610 and the position of the end of the optical waveguideshifting.

Within telecommunication architectures such as those supporting the fullservice access network many variants of passive optical networks (PONs)have been considered. Amongst, these are next generation PONarchitectures exploiting WDM and TDM such as the cost called NextGeneration PON stage 2 (NG-PON2) which exploits a coloured optical lineterminal (OLT) coupled to an optical distribution network (ODN) withcolorless optical network units (ONUs) coupled to the distributive ODN.In such networks colorless implies that the ONU or other elementoperates over a range of optical wavelengths without requiring thenetwork operator to select and deploy wavelength specific (coloured)components/devices. One approach is the exploitation of small freespectral range components whilst another is to deploy wavelengthtunable/settable components. Within an NG-PON2 the OLT determines thebandwidth and wavelength for each ONU such that both the receiver andthe transmitter within the ONU must be wavelength settable.

Now referring to FIG. 27A there is depicted such an 8-wavelength tunableONU according to an embodiment of the invention for an NG-PON2application employing a dual-band transceiver circuit 2700A exploiting apair of wavelength selective MOTUS optical engines 2710 and 2715respectively. As depicted the transceiver circuit 2700A is coupled to anoptical fiber 2750 and comprises a band filter circuit 2760 whichreceives a L-band wavelength signal from second wavelength selectiveMOTUS optical engine 2715 and couples it to the optical network via theband filter circuit 2760 whilst C-band optical signals from the opticalnetwork are coupled from the band filter circuit 2715 to the firstwavelength selective MOTUS optical engine 2710. The first wavelengthselective MOTUS optical engine 2710 employs transmissive filters, suchas described and depicted in respect of the WSR 2200 in FIG. 22, withintransmissive filter array 2790 which are coupled to a photodetectorcircuit 2740 via first combiner circuit 2720. Accordingly, the selectedC-band channel is filtered and coupled to a receive photodetector withinphotodetector circuit 2740.

In contrast the second wavelength selection MOTUS optical engine 2715employs an array of reflective filters 2780 in combination with areflective SOA (RSOA) element 2770 to form a wavelength selectiveresonating cavity wherein the resulting wavelength specific output fromthe high reflectivity facet of the RSOA element 2770 is coupled via aMach-Zehnder modulator 2765 to the band filter circuit 2760 and thereinto the optical fiber 2750. The outputs from the array of reflectivefilters 2780 are combined via second combiner circuit 2725 and coupledto photodetector circuit 2740. Optical alignment within the transceivercircuit 2700A is provided via first to fourth MEMS actuators 2730A to2730D wherein these respectively provide:

-   -   Alignment from first combiner circuit 2720 to the optical        waveguide coupling to the photodetector circuit 2740;    -   Alignment from second combiner circuit 2725 to the optical        waveguide coupling to the photodetector circuit 2740;    -   Alignment between optical waveguide coupled to second wavelength        selection MOTUS optical engine 2715 and RSOA element 2770; and    -   Alignment between high reflectivity facet of RSOA element 2770        and optical waveguide coupling to the Mach-Zehnder modulator        2765.

For example, first and second combiner circuits 2720 and 2725 may employa tree-structure of directional coupler wavelength division multiplexers(WDMs) and/or Mach-Zehnder interferometer WDMs as well as single tomultimode couplers, array waveguide grating (AWG) WDMs etc. Thephotodetector circuit 2740 may be implemented within the same siliconcircuit as the passive optical waveguides, transmissive and reflectivewavelength filters, first and second wavelength selective MOTUS opticalengines 2710 and 2715 etc. The photodetector circuit 2740 comprises ahigh speed photodetector for the received data on the C-band opticalsignal filtered and a low speed photodetector for the outputs from thearray of reflective filters 2780 within the L-band. Alternatively, thephotodetector circuit 2740 may be an InP die flip-chipped to thetransceiver circuit 2700A with or without additional actuators foralignment depending upon the alignment tolerances of the opticalphotodetector(s). The RSOA element 2770 would be an InP die flip-chippedto the transceiver circuit 2700A.

Now referring to FIG. 27B there is depicted such a 4-wavelength tunableONU according to an embodiment of the invention for an NG-PON2application employing a dual-band transceiver circuit 2700B exploiting apair of wavelength selective MOTUS optical engines 2710 and 2715respectively. As depicted the dual-band transceiver circuit 2700Breceives a downstream (DS) band signal between 1596-1603 nm whilsttransmitting an upstream (UP) band signal between 1524-1544 nm.Accordingly, the network connection is made via an optical filtercircuit 27010 comprising a directional coupler and DS/UP Bragg filter.The DS band signal is coupled and selected via the first wavelengthselective MOTUS optical engines 2710 and transmissive optical filters27070 to first optical photodetector 27030A via first combiner circuit27020A. The UP band signal is coupled to the network via optical filtercircuit 27010 having been generated via a tunable optical sourcecomprising RSOA element 2770 with second wavelength selective MOTUSoptical engines 2715 in conjunction with Bragg reflective filter array27080 and wavelength locker 27060. The tunable optical source hasdisposed within a tap coupler 27040 which couples via a Mach-Zehndermodulator 27050 to the optical filter circuit 27010. The outputs fromthe Bragg reflective filter array 27080 are coupled via second combinercircuit 27020B to second optical photodetector 27030B.

Also depicted within dual-band transceiver circuit 2700B in FIG. 27B isa MEMS OWMP 27090 according to an embodiment of the invention disposedbetween the first combiner circuit 27020A on the output opticalwaveguide and coupling it to the second optical photodetector 27030B. Assuch the MEMS OWMP 27090 can perform micro-positioning for alignmenttolerances of the flip-chip mounting of the optical photodetector27030B, e.g. an avalanche photodiode (APD), but also perform opticalpower management under controller feedback to limit and/or avoidsaturation of the APD under higher optical powers received at thedual-band transceiver circuit 2700B.

Within dual-band transceiver circuit 2700B the optical filter circuit27010 may be replaced by a directional coupler. Any upstream signalsreflected within the network are isolated from the transmitter throughthe split ratio of the tap coupler 27040 in conjunction with double passexcess loss of the Mach-Zehnder modulator 27050 and double pass excessloss of the coupler at the front-end of the dual-band transceivercircuit 2700B. Within other transceivers WDM components for coupling theupstream/downstream signals from and to the transceiver.

Now referring to FIG. 28A there is depicted a 4-wavelength tunable ONUaccording to an embodiment of the invention for a next generationtelecommunications network application employing a dual-band transceivercircuit 2800 exploiting a pair of wavelength selective MOTUS opticalengines 2710 and 2715 respectively such as described supra in respect ofFIG. 27B. First wavelength selective MOTUS optical engine 2710 beingcoupled to the downstream channel and providing wavelength filtering butrather than being coupled to a single APD the wavelength filtered outputis coupled to a coherent receiver circuit 2820 comprising a polarizationsplitter and a pair of APDs for mixing of the received optical signalwith a local oscillator for phase and/or frequency keyed data to bedownconverted. The second wavelength selective MOTUS optical engine 2715forms part of a wavelength tunable upstream transmitter employingreflective Bragg gratings in combination with an OSA and wavelengthlocker such as described in FIG. 27B. However, the dual-band transceivercircuit 2800 now also comprises third wavelength selective MOTUS opticalengine 2810 which in conjunction with reflective OSA 2820 and Braggfilter array 2830 to provide wavelength tunable optical source 2850 toprovide the local oscillator (LO) for the coherent receiver circuit2820.

Now referring to FIG. 28B there is depicted a 4-wavelength tunable ONUaccording to an embodiment of the invention for a next generationtelecommunications network application employing a dual-band transceivercircuit 2800B which is configured essentially the same as the4-wavelength tunable ONU described and depicted in dual-band transceivercircuit 2800 in FIG. 28A except that it supports bidirectionalQuadrature Phase Shift Keying (QPSK) communications through QPSKmodulator 2860 on the upstream channel and coherent QPSK detectorcircuit 2870 on the downstream channel.

In contrast to other wavelength tunable lasers within other transmittersand transceivers the LO should provide both TE and TM polarisations suchthat incoming variations in the state of polarization do not result inreceiver signal fade as the LO and received signal become orthogonal inpolarization. This can be achieved either through design of the opticalwaveguides in conjunction with the OSA or through employing apolarization scrambler/rotator/gratings such as known in the prior artemploying, for example, dual core waveguides. Optionally, dualpolarizations may be exploited as dual carriers such that dualpolarization (DP) transmission may be undertaken with each polarizationencoded using quadrature phase shift keying (QPSK), for example, toprovide DP-QPSK modulation.

Now referring to FIGS. 29A and 29B there are depicted first and secondwavelength selective filters 2900A and 2900B respectively according toan alternate waveguide to wavelength selective filter coupling mechanismaccording to embodiments of the invention exploiting direct waveguidecoupling from the tilted beam of a MEMS actuator. Referring to FIG. 29Aand first wavelength selective filter 2900A an array of Bragg gratings2950 are depicted as discussed and described supra in respect ofembodiments of the invention. In contrast to the MOEMS mirror aninput/output waveguide 2910 becomes unsupported waveguide 2940 and isdisposed upon free standing beam 2930 which is coupled to the actuatorbeam 2935 of a MEMS actuator comprising first and second electro-staticMEMS actuators 2920A and 2920B respectively such as described supra inrespect of embodiments of the invention. Accordingly, rotation of thefirst and second electro-static MEMS actuators 2920A and 2920Brespectively rotates the actuator beam 2935 and therein the beam 2930based upon its pivot point, the pivot not being depicted for clarity.Accordingly, the waveguide end facet of waveguide 2940 is rotated andaligned to one of the Bragg gratings 2950 wherein the reflected signalis coupled back as described in other embodiments of the inventionexploiting reflective Bragg grating structures. It would be apparentthat in other embodiments of the invention the reflective Bragg filtersmay be transmissive Bragg filters coupling to other waveguides at theirdistal ends away from the MOEMS structure or that Fabry-Perot filtersmay be employed. Optionally, no wavelength selective elements arepresent allowing the structure to operate as an 1×N optical switch.Optionally, rather than first and second electro-static MEMS actuators2920A and 2920B respectively being rotational actuators these are linearactuators based upon appropriate positioning of the pivot point.Optionally, a single actuator may be employed.

Now referring to FIG. 29B and second wavelength selective filter 2900Ban array of Bragg gratings 2950 are depicted as discussed and describedsupra in respect of embodiments of the invention. In contrast to theMOEMS mirror an input/output waveguide 2980 becomes unsupportedwaveguide 2990 and is disposed upon free standing beam 2970 which iscoupled to a MEMS actuator 2960 such as described supra in respect ofembodiments of the invention exploiting rotary electro-static actuation.Accordingly, rotation of the electro-static MEMS actuator 2960 rotatesthe free standing beam 2970 based upon its pivot point, the pivot notbeing depicted for clarity. Accordingly, the waveguide end facet ofwaveguide 2990 is rotated and aligned to one of the Bragg gratings 2950wherein the reflected signal is coupled back as described in otherembodiments of the invention exploiting reflective Bragg gratingstructures. It would be apparent that in other embodiments of theinvention the reflective Bragg filters may be transmissive Bragg filterscoupling to other waveguides at their distal ends away from the MOEMSstructure or that Fabry-Perot filters may be employed. Optionally, nowavelength selective elements are present allowing the structure tooperate as an 1×N optical switch. Within second wavelength selectivefilter 2900B the optical waveguide has been depicted absent the silicondioxide layer for clarity.

It would be evident to one skilled in the art that the first and secondwavelength selective filters 2900A and 2900B in FIGS. 29A and 29Brespectively may be employed in the MOEMS optical circuits describedsupra in respect of receivers, transmitters, and transceivers withinFIGS. 1 through 28 respectively.

Now referring to FIG. 30 there is depicted an alternate exemplary MOTUSoptical engine 3000 according to an embodiment of the inventionemploying a MEMS tuned grating 3030 for wavelength selective reflection.Accordingly, an input/output three-dimensional (3D) optical waveguide3060 couples to/from a short planar waveguide region before coupling toa planar (two dimensional or 2D) waveguide which forms part of asemi-circular (SC) MEMS 3040 such as described supra in respect ofembodiments of the invention. The SC-MEMS 3040 is coupled to anelectro-static actuator 3010 such that movement of the electro-staticactuator 3010 results in rotation of the SC-MEMS 3040 through the pivotpoint defined by the MEMS anchor 3010. However, rather than the rotationof the SC-MEMS 3040 adjusting the point at which the input/outputwaveguide 3060 is re-imaged laterally to another waveguide the rotationof the SC-MEMS 3040 rotates the grating 3030 such that the wavelengthreflected back to the input/output optical waveguide 3060 is adjusted.It would be evident that the grating 3030 within the planar (2D) opticalwaveguide on the surface of the SC-MEMS 3040 may be an echelle grating,echelon grating, or other reflective grating employing a plurality ofdistributed reflectors with offsets.

Optionally, the grating 3030 may also be formed upon the rear surface ofthe SC-MEMS 3030 rather than within the planar waveguide itself whichmay remove an additional lithography and etching sequence within themanufacturing flow. Optionally, the MEMS tuned waveguide grating opticalrouting described and depicted with respect to FIG. 30 may be employedwithin the other MOTUS optical engines described and addressed withinthis specification for wavelength selective filtering (eithertransmissive or reflective) and optical routing.

Within the embodiments of the invention described supra in respect ofFIGS. 1 to 30 thin silicon and/or silicon nitride optical waveguideshave been described. However, it would be evident that other embodimentsmay exploit thicker silica or silicon nitride or silicon oxynitridewaveguide technologies in addition to others such as polymeric etc.Accordingly, thicker polarization independent optical waveguides may beemployed as well as allowing implementation of athermal Bragg gratings.

Whilst embodiments of the invention described supra in respect of FIGS.1 to 29B have been described primarily from the perspective of 1550 nmcommunications with C-band/L-band operation it would be evident thatother embodiments may be implemented including those supporting theS-band, only C-band with band-splitting, only L-band withband-splitting, 1310 nm operation, and O-band operation and/orcombinations thereof.

Within embodiments of the invention described above in respect of theFigures then it would be evident that an air gap is provided between theSC-MEMSM and the remaining optical circuit in order to allow theSC-MEMSM to freely rotate. However, once the wavelength is set it willtypically be left at that wavelength for a significant period of timewhereby removal of the requirement to maintain electrostatic actuationmay be beneficial. Accordingly, within embodiments of the invention theSC-MEMSM is employed in conjunction with a linear actuator that pushesthe SC-MEMSM towards the waveguides thereby reducing the gap oreliminating it such that friction may keep the SC-MEMSM in position.

Within other embodiments of the invention the upper surface of theSC-MEMS may have features formed upon it that the opposite shape tofeatures formed on the upper surface of the optical waveguide section ofthe MOTUS. These may be formed, for example, using a metal depositedonto these surfaces whilst the air gap is filled within a sacrificialmaterial, e.g. parylene, allowing one of the feature upon the SC-MEMSMor optical waveguide section to project forward of the optical sidewall.In this manner as the SC-MEMSM is moved forward under the action of alinear actuator then these features act to align the SC-MEMSM by theiralignment and geometry. These features may therefore act to limit thesubsequent lateral / rotational movement of the SC-MEMSM.

Within other embodiments of the invention the SC-MEMSM may be latchedonce set to the appropriate location. Such latching may, for example, beprovided by a latching mechanism forming part of the lateral actuator oralternatively the latching may be achieved through a coupling anotherMEMS structure to the SC-MEMSM. Such a coupling may for example be adeformation of a MEMS formed above or adjacent to the SC-MEMSM to locateagainst a feature within the vertical surface of the SC-MEMSM or thesidewall of the SC-MEMS. With the knowledge of the rotation of theSC-MEMSM to one of a series of predetermined locations to align to thewaveguides containing wavelength selective transmissive or reflectivestructures these features to latch the SC-MEMSM may be in predeterminedlocations.

Within other embodiments of the invention once the SC-MEMSM has beenaligned to the appropriate waveguide then gripping latching actuatorsmay grip the electrostatic actuators rotating the SC-MEMSM.

Within embodiments of the invention described above in respect of theFigures then it would be evident to one skilled in the art that theseare specific but non-limiting embodiments. However, in other embodimentsof the invention:

-   -   the Bragg gratings may be employed to filter forward propagating        signals that proceed to other portions of the optical circuit        and/optical system;    -   the Bragg gratings may be employed to reflect a predetermined        portion and propagate the remainder;    -   optical filters contained in waveguides selected by the MEMS        could be something else than a Bragg grating: e.g., Fabry-Perot        cavities, ring resonators, photonic crystal, etc.    -   optical filters may be grating based such as echelle and        echelon;    -   the SC-MEMSM mirror and/or the optical circuit may couple to        free space optics rather than waveguide optical circuit        elements;    -   the SC-MEMSM mirror may scan an optical signal;    -   the Bragg gratings may be formed using other techniques than        cladding modulated first order gratings including, but not        limited to, waveguide width variations, different optical        materials, doping, ion implantation, and photoinduced refractive        index variations;    -   the Bragg gratings may be uniform, sampled, apodized, chirped,        and tilted.

Within embodiments of the invention described above in respect of theFIGS. 1 then it would be evident to one skilled in the art that theembodiments have been described with respect to particularconfigurations. However, in other embodiments of the invention andwavelength tunable transmitters, receivers, and transceivers the Bragggratings may be:

-   -   sequential in wavelength across the device;    -   pseudo-randomly sequenced; and    -   according to a predetermined wavelength plan;

Within embodiments of the invention described above in respect of theFigures then it would be evident to one skilled in the art that theseare specific but non-limiting embodiments. However, in other embodimentsof the invention:

-   -   exploit multiple SC-MEMSM elements for increased angular range;    -   exploit paired SC-MEMSM elements to select/deselect a specific        wavelength in different portions of an optical device;    -   exploit additional optical elements within the planar waveguide;    -   collimating/focusing transmissive grating;    -   collimating/focusing reflective grating;    -   polarizers;    -   multiple optical amplifiers coupling to multiple channel        waveguides;    -   machined waveguide lens;    -   index induced waveguide lens;    -   waveguide Fresnel lens; and    -   other variable optical properties of materials adjusted through        mechanical transformation at sub-wavelength scales may be        employed such as arising from compression, expansion,        deformation, etc. of optically transparent media.

Within embodiments of the invention described above in respect of theFigures then it would be evident to one skilled in the art that theseare specific but non-limiting embodiments. However, in other embodimentsof the invention:

-   -   fluorinated polymers may be employed on the air gap facets of        the waveguides for anti-reflection coatings;    -   the Bragg gratings within silicon nitride cored waveguides may        be athermal or exhibit significantly reduced thermal wavelength        shift, and    -   that the MOTUS optical engine may be designed for operation at a        predetermined elevated temperature allowing removal of cooling        requirements within the assembled package    -   that the MOTUS optical engine may be packaged with an external        thermal heater to ensure that it operates at the desired        elevated temperature.    -   that the MOTUS optical engine designed for operation at a        predetermined elevated temperature may use the thermal        dissipation requirements of the gain element in lieu or        combination with the external thermal heater.

Specific details are given in the above description to provide athorough understanding of the embodiments. However, it is understoodthat the embodiments may be practiced without these specific details.For example, circuits may be shown in block diagrams in order not toobscure the embodiments in unnecessary detail. In other instances,well-known circuits, processes, algorithms, structures, and techniquesmay be shown without unnecessary detail in order to avoid obscuring theembodiments.

The foregoing disclosure of the exemplary embodiments of the presentinvention has been presented for purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Many variations andmodifications of the embodiments described herein will be apparent toone of ordinary skill in the art in light of the above disclosure. Thescope of the invention is to be defined only by the claims appendedhereto, and by their equivalents.

Further, in describing representative embodiments of the presentinvention, the specification may have presented the method and/orprocess of the present invention as a particular sequence of steps.However, to the extent that the method or process does not rely on theparticular order of steps set forth herein, the method or process shouldnot be limited to the particular sequence of steps described. As one ofordinary skill in the art would appreciate, other sequences of steps maybe possible. Therefore, the particular order of the steps set forth inthe specification should not be construed as limitations on the claims.In addition, the claims directed to the method and/or process of thepresent invention should not be limited to the performance of theirsteps in the order written, and one skilled in the art can readilyappreciate that the sequences may be varied and still remain within thespirit and scope of the present invention.

What is claimed is:
 1. A device comprising: a substrate; an opticalwaveguide structure comprising: a plurality of first three-dimensional(3D) optical waveguides disposed upon the substrate; a second 3D opticalwaveguide disposed upon the substrate; a third 3D optical waveguidedisposed upon a beam having a first end disposed at a first end of thebeam and a second distal end disposed at a second distal end of thebeam; the beam having its first end coupled to the substrate and itssecond distal end isolated from the substrate allowing it to moverelative to the substrate; a rotational microoptoelectromechanical(MOEMS) element comprising the beam, a pivot and an actuator; wherein apredetermined rotation of the rotational MOEMS element under the motionof the actuator results in an alignment of the second distal end of thethird 3D optical waveguide with a first end of a predetermined first 3Doptical waveguide of the plurality of first 3D optical waveguides; andthe second 3D optical waveguide is optically coupled to the third 3Doptical waveguide at the first end of the beam.
 2. The device accordingto claim 1, wherein a portion of each first 3D optical waveguide of theplurality of first 3D optical waveguides is a transmissive wavelengthfilter.
 3. The device according to claim 1, wherein a portion of eachfirst 3D optical waveguide of the plurality of first 3D opticalwaveguides is a reflective wavelength filter.
 4. The device according toclaim 1, wherein the actuator is an electro-static actuator disposedlaterally to one side of the beam; the actuator is mechanically coupledto the beam by an actuator beam; the actuator beam is coupled to thebeam at a predetermined point between the first end of the beam and asecond end of the beam; and the pivot of the rotational MOEMS element isdisposed at the predetermined point upon the beam coupled to theactuator beam.
 5. The device according to claim 1, wherein the actuatorcomprises: a first electro-static actuator disposed to one side of thebeam; a second electro-static actuator disposed to a second side of thebeam distal to the first electro-static actuator; and an actuator beamcoupled at a first end to the first electro-static actuator and at asecond distal end to the second electro-static actuator; the actuatorbeam is coupled to the beam at a predetermined point between the firstend of the beam and a second end of the beam; and the pivot of therotational MOEMS element is disposed at the predetermined point upon thebeam coupled to the actuator beam.
 6. The device according to claim 1,wherein a portion of each first 3D optical waveguide of the plurality offirst 3D optical waveguides is a transmissive wavelength filter; asecond distal end of each first 3D optical waveguide of the plurality offirst 3D optical waveguides is coupled to a unique predeterminedphotodetector of a plurality of photodetectors.
 7. The device accordingto claim 1, wherein a portion of each first 3D optical waveguide of theplurality of first 3D optical waveguides is a transmissive wavelengthfilter; the optical waveguide structure further comprises a plurality ofmultimode interferometers and a plurality of photodetectors; a seconddistal end of each first 3D optical waveguide of a predetermined subsetof the plurality of first 3D optical waveguides is coupled to an inputside of a predetermined multimode interferometer of the plurality ofmultimode interferometers; and each photodetector of the plurality ofphotodetectors is optically coupled to an output side of a predeterminedmultimode interferometer of the plurality of multimode interferometers.8. The device according to claim 1, wherein the optical waveguidestructure further comprises a lens and a fourth 3D optical waveguidedisposed upon the substrate; a first side of the lens is opticallycoupled to the second distal end of each first 3D optical waveguide ofthe plurality of first 3D optical waveguides; and a second side of thelens is optically coupled to the fourth 3D optical waveguide.
 9. Thedevice according to claim 1, wherein the optical waveguide structurefurther comprises a two-dimensional (2D) optical waveguide disposed uponthe substrate; and the 2D optical waveguide is disposed between thesecond distal end of the third 3D optical waveguide and the first end ofeach first 3D optical waveguide of the plurality of first 3D opticalwaveguides.
 10. A device comprising: a substrate; a rotationalmicrooptoelectromechanical (MOEMS) element comprising a pivot, anactuator and a beam having a first end disposed to one side of the pivotand coupled to the actuator and a second distal end disposed to anotherside of the anchor to that of the actuator; an optical waveguidestructure comprising: a plurality of first three-dimensional (3D)optical waveguides disposed upon the substrate; a second 3D opticalwaveguide disposed upon the substrate having an end disposed upon theanchor; a third 3D optical waveguide disposed upon that portion of thebeam between the second distal end of the beam and the anchor having afirst end at the second distal end of the beam and a second distal endat the anchor; a predetermined rotation of the rotational MOEMS elementunder the motion of the actuator results in an alignment of the firstend of the third 3D optical waveguide with a first end of apredetermined first 3D optical waveguide of the plurality of first 3Doptical waveguides; and the second 3D optical waveguide is opticallycoupled to the third 3D optical waveguide at the anchor.
 11. The deviceaccording to claim 10, wherein a portion of each first 3D opticalwaveguide of the plurality of first 3D optical waveguides is atransmissive wavelength filter.
 12. The device according to claim 10,wherein a portion of each first 3D optical waveguide of the plurality offirst 3D optical waveguides is a reflective wavelength filter.
 13. Thedevice according to claim 10, wherein the actuator is an electro-staticactuator; the actuator is mechanically coupled to the beam by anactuator beam; the actuator beam is coupled to the beam at apredetermined point between the first end of the beam and a second endof the beam; and the pivot of the rotational MOEMS element is disposedat the predetermined point upon the beam coupled to the actuator beam.14. The device according to claim 10, wherein a portion of each first 3Doptical waveguide of the plurality of first 3D optical waveguides is atransmissive wavelength filter; a second distal end of each first 3Doptical waveguide of the plurality of first 3D optical waveguides iscoupled to a unique predetermined photodetector of a plurality ofphotodetectors.
 15. The device according to claim 10, wherein a portionof each first 3D optical waveguide of the plurality of first 3D opticalwaveguides is a transmissive wavelength filter; the optical waveguidestructure further comprises a plurality of multimode interferometers anda plurality of photodetectors; a second distal end of each first 3Doptical waveguide of a predetermined subset of the plurality of first 3Doptical waveguides is coupled to an input side of a predeterminedmultimode interferometer of the plurality of multimode interferometers;and each photodetector of the plurality of photodetectors is opticallycoupled to an output side of a predetermined multimode interferometer ofthe plurality of multimode interferometers.
 16. The device according toclaim 10, wherein the optical waveguide structure further comprises alens and a fourth 3D optical waveguide disposed upon the substrate; afirst side of the lens is optically coupled to the second distal end ofeach first 3D optical waveguide of the plurality of first 3D opticalwaveguides; and a second side of the lens is optically coupled to thefourth 3D optical waveguide.
 17. The device according to claim 10,wherein the optical waveguide structure further comprises atwo-dimensional (2D) optical waveguide disposed upon the substrate; andthe 2D optical waveguide is disposed between the second distal end ofthe third 3D optical waveguide and the first end of each first 3Doptical waveguide of the plurality of first 3D optical waveguides.